Spatiotemporal Seismic Hazard and Risk Assessment of Global M9.0 Megathrust Earthquake Sequences

  • Lizhong Zhang

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Megathrust earthquake sequences can impact multiple buildings and infrastructure in a city/municipality due to not only the mainshock but also the triggered aftershocks along the subduction interface and in the overriding crust. The time between the mainshocks and aftershocks usually is too short to retrofit the structures; therefore, aftershocks can cause additional damage. To have a better understanding of the impact of aftershocks on city-wide seismic risk assessment, this thesis develops a new simulation framework of spatiotemporal seismic hazard and risk assessment of future M9.0 sequences. Different components under the new simulation framework including the seismicity model and the fragility model are developed.
The epidemic type aftershock sequence (ETAS) model, a spatiotemporal seismicity model, is modified to characterise aftershocks of large and anisotropic finite M9.0 mainshock sources. To give realistic ranges of aftershock simulations in regions with limited data after a future giant shock, the variability of the ETAS model parameters is assessed in global subduction zones that have experienced M≥7.5 earthquakes. Considering known biases of the parameters (due to model formulation, the isotropic spatial distribution, and finite-size effects of catalogues), the variability of the ETAS parameters from robust estimates is not significant. A set of ETAS parameters of future M9.0 sequences is proposed for hazard assessment.
Cascadia subduction zone is considered as a case study to demonstrate how the new simulation framework can be applied to a subduction-zone region with limited observed data. To account for damage accumulation of wood-frame houses due to aftershocks in Canada, a new approach that adopts cloud analysis using real mainshock-aftershock sequences with moderate scaling factors is proposed to develop state-dependent fragility curves. By implementing the updated components of the spatiotemporal seismicity model and the state-dependent fragility model, the simulation framework can be used for quasi real-time aftershock hazard and risk assessments and post-event risk management.
Date of Award24 Mar 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorFlavia De Luca (Supervisor) & Max Werner (Supervisor)

Keywords

  • Spatiotemporal seismic hazard and risk assessment of megathrust sequences
  • Spatiotemporal ETAS model
  • M9.0 megathrust events triggering crustal and subduction aftershocks
  • Global subduction zones
  • State-dependent aftershock fragility curves of wood-frame houses
  • Damage state estimation of spatially distributed wood-frame houses

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